Glen Canyon Dam Update

Basin Hydrology

Severe drought conditions in the Colorado River Basin continue. As we move into mid-winter, there are no clear signals that the drought is easing. While much of Utah was slammed with a major winter storm the last week of December, snowpack in the Colorado River Basin remains near average. The bulk of the moisture from the Utah storm was in the Wasatch Mountains,west of the Colorado River Basin. As of December 30, 2003, snowpack in the Colorado River Basin is 101 percent of average. Because of the extended drought, the snowpack lies atop a mantle of very dry soil. This scenario is not favorable for next springs runoff, as much of the melting snow will be absorbed by the soil. Reclamation is estimating that with average snowpack conditions this winter, runoff next spring would be about 75 percent of average. The National Weather Service will issue an April through July inflow forecast for Lake Powell on January 5, 2004.

The Colorado River Basin is now in its 5th year of drought. Inflow volumes have been below average for 4 consecutive years. Unregulated inflow in water year 2003 was only 53 percent of average. Unregulated inflow in 2000, 2001 and 2002 was 62, 59, and 25 percent of average, respectively. Inflow in 2002 was the lowest ever observed since the completion of Glen Canyon Dam in 1963.

The trend of low inflow continues. Unregulated inflow in November, 2003 was 64 percent of average and Decembers will likely end up at about 65 percent of average. On December 29, 2003 observed inflow to Lake Powell was 5,000 cfs, about 60 percent of what is usually seen in late December.

Low inflows have reduced water storage in Lake Powell. On December 5, 2003, the elevation of Lake Powell dropped below 3600 feet. The last time the water surface elevation was this low was in 1973. The current elevation (as of December 30, 2003) of Lake Powell is 3,597 feet (103 feet from full pool). Current storage is 11.5 million acre-feet (47 percent of capacity). The good news is that even after 4 years of severe drought Lake Powell is still storing a large volume of water.

Operations Experimental Flows

Daily high fluctuating releases from Glen Canyon Dam, as part of the Glen Canyon Dam experimental flows, will be implemented from January through March 2003. Releases will range between a high of 20,000 cubic feet per second (cfs) to a low of 5,000 cfs each day. The 20,000 cfs releases will be maintained for about 9 hours each day (from about 11:00 am until about 8:00 pm), while the 5,000 cfs releases will be maintained for about 8 hours (from about 1:00 am until about 9:00 am). The remainder of the hours will be transition releases where releases will be between the daily high and the daily low. This pattern will be maintained for 7 days a week during the January through March time period. It should be noted that due to real-time power considerations and regulation to stabilize the power system, actual releases may deviate somewhat from this pattern

The January through March high fluctuating releases are intended to benefit the endangered humpback chub. Scientists have recognized that the humpback chub population has been in general decline since highly fluctuating flows were curtailed in November of 1991. Those flows helped keep the non-native fish, especially the rainbow and brown trout, in check. The trout are thought to prey upon and compete with native fish such as the endangered humpback chub. This is the second year of high fluctuating releases as part of the experimental flows. High fluctuating releases were first implemented in January through March of 2003.

Monthly release volumes in January, February, and March 2003 are scheduled to be 788, 737, and 788 thousand acre-feet, respectively, which averages out to 12,800 cfs per day. Because of the draw down condition of Lake Powell, releases from Lake Powell in water year 2004 are being scheduled to meet the minimum release objective of 8.23 million acre-feet. This is consistent with the requirements of the Criteria for Coordinated Long-Range Operation of Colorado River Reservoirs. The experimental flows will not change the total volume of water to be released from Lake Powell in water year 2004.

The experimental flows from Glen Canyon Dam received environmental clearances in December 2002. The flows were analyzed in an environmental assessment in accordance with the National Environmental Policy Act. The experimental flows are the result of ongoing studies by scientists from the United States Geological Survey and were recommended by the Glen Canyon Dam Adaptive Management Work Group, a Federal advisory committee. The experimental flows address the decline of two key resources in the Grand Canyon: sediment and population viability of endangered humpback chub. The Finding of No Significant Impact on the experimental flows can be found at

This release courtesy Tom Ryan.